JP5387037B2 - Ink set, recording apparatus, and recording method - Google Patents

Description

  The present invention is an ink set in which the color reproduction area (gamut) is enlarged, and in particular, the color reproduction area in the dark blue area is enlarged, and the color reproduction in other color areas is also excellent. It relates to an ink set. The present invention also relates to a recording apparatus and a recording method using the ink set.

As one of color models, the CIE / L ^* a ^* b ^* color system is known. According to the CIE / L ^* a ^* b ^* , all colors (spectrums) in the visible light region that can be observed by humans can be expressed by chromaticity coordinates.
Among the three parameters (L ^* , a ^* , b ^* ) of the CIE / L ^* a ^* b ^* color system, L ^* is the luminance (brightness) of the color, and a ^* and b ^* are the hue and saturation. Indicates the chromaticity shown. Here, when L ^* = 0, it represents black and L ^* = 100 represents white. Further, a ^* represents a position between the colors red and green, a negative value indicates green, and a positive value indicates red. b ^* represents the position between the colors yellow and blue, with negative values indicating blue and positive values indicating yellow. Since the L ^* a ^* b ^* color model is three-dimensional, the color space is represented in three-dimensional space, and the luminance is represented on the vertical axis.

However, the L ^* a ^* b ^* color model is an index used to conceptually describe the color space, and its color reproduction range is limited. That is, for example, when an image is formed on a recording medium using a pigment-based ink or ink set, there are colors that cannot be reproduced depending on the color of the L ^* a ^* b ^* color model.

  On the other hand, ink compositions containing various pigments having high color developability have been proposed. In Patent Document 1, an ink composition including a quinacridone solid solution pigment, a polyether-modified polydimethylsiloxane compound, and water has high color developability, and ink reliability such as ejection stability, storage stability, and clogging. It is disclosed that an ink having excellent properties can be obtained. In Patent Document 2, a surface-treated pigment (yellow, magenta, cyan) in which a hydrophilic dispersing group is bonded to the surface of a solid solution pigment formed from two or more specific pigments, a water-insoluble vinyl polymer, In addition, it is described that an ink having excellent ink reliability such as printing quality, ejection stability, storage stability, and clogging can be realized by an ink composition containing water.

JP 2006-282810 A JP 2007-186661 A

By the way, conventionally, there is a limit to color reproduction in a blue region in a dark portion where an L ^* value is 20 or less. That is, since it is difficult to express chromaticity and saturation when the luminance is low, for example, (L ^* , a ^* , b ^* ) = (19.4, 30.0) in the CIE / L ^* a ^* b ^* color system , −72.6) and (L ^* , a ^* , b ^* ) = (19.4, 37.6, −76.8), the L ^* value is 20 or less, and the a ^* value is 30. As described above, it has been impossible to reproduce a color having a b ^* value of −75 or less on an image recording medium with droplets (ink). On the other hand, the inventors of the present invention diligently studied to enlarge the color reproduction range of the dark blue region, and in the prior application Japanese Patent Application No. 2008-215506, C.I. I. Pigment blue 15: 6 or C.I. I. By combining a cyan ink composition containing Pigment Blue 60 as a pigment and a magenta ink composition containing a quinacridone pigment into an ink set, a color reproduction range in a dark blue region having an L ^* value of 20 or less is achieved. The ability to expand, and in particular C.I. I. When a cyan ink composition containing Pigment Blue 15: 6 as a pigment is combined with a magenta ink composition containing a quinacridone solid solution pigment to form an ink set, an L ^* value of 20 or less, which has been impossible to reproduce in the past, has been impossible. , A ^* value of 30 or more and b ^* value of −75 or less can be realized.

  On the other hand, as the ink set, when the cyan ink composition and the magenta ink composition are mixed, the color of the blue region is used. When the yellow ink composition and the magenta ink composition are mixed, the color of the red region is used. In general, when the yellow ink composition and the cyan ink composition are mixed, the color in the green region is reproduced. Therefore, when the color reproducibility of the blue area is expanded, the color reproduction in the green area reproduced with the cyan ink composition and the yellow ink composition, and the red area reproduced with the yellow ink composition and the magenta ink composition. For example, it is necessary to make the color reproduction range compatible with other color areas. On the other hand, the present inventors have included C.I. I. Although Pigment Blue 60 is an effective pigment species for expanding the reproduction range of the dark blue region, it has been found that the color developability of the green region is greatly reduced. Japanese Patent Application No. 2008-232165 , C.I. I. A cyan ink composition containing CI Pigment Blue 15: 6 as a pigment; I. Pigment violet 19, C.I. I. Pigment red 122, C.I. I. Pigment red 202 and C.I. I. A magenta ink composition comprising a quinacridone pigment selected from the group consisting of CI Pigment Red 209 or a quinacridone solid solution pigment formed from at least two selected from the group; I. Pigment yellow 74, C.I. I. Pigment yellow 213 and C.I. I. It has been proposed that by combining with a yellow ink composition containing a pigment selected from the group consisting of CI Pigment Yellow 185, an ink set can achieve both color reproducibility in the blue region and the green region.

  However, the present inventors have recently found that C.I. contained in the cyan ink composition as a pigment. I. It has been found that Pigment Blue 15: 6 is inferior in graininess when recording an image in a high brightness area. Generally, an ink set is composed of a cyan ink composition, a magenta ink composition, a yellow ink composition, a light cyan ink composition, and a light magenta ink composition. In order to improve the property, an ink composition (light ink composition) having a low pigment concentration is used among the ink compositions of similar colors in the ink set. However, C.I. I. It has been found that in the high brightness cyan area and the green area where image recording is performed using a light cyan ink composition containing Pigment Blue 15: 6 as a pigment, there is a problem in graininess such that dots are easily noticeable.

Accordingly, an object of the present invention is to provide an ink set in which a color reproduction region (gamut) is enlarged and excellent in graininess in a high brightness region.
Another object of the present invention is to provide a recording method and a recording apparatus using the ink set.

This invention is made | formed based on the said knowledge, and is as follows.
(1) C.I. I. A cyan ink composition containing Pigment Blue 15: 6 as a pigment;
C. I. Pigment violet 19, C.I. I. Pigment red 122, C.I. I. Pigment red 202 and C.I. I. A magenta ink composition comprising a quinacridone pigment selected from the group consisting of CI Pigment Red 209 or a quinacridone solid solution pigment formed from at least two selected from the group;
C. I. Pigment yellow 74, C.I. I. Pigment yellow 213 and C.I. I. A yellow ink composition comprising a pigment selected from the group consisting of CI Pigment Yellow 185;
C. I. Pigment violet 19, C.I. I. Pigment red 122, C.I. I. Pigment red 202 and C.I. I. A light magenta ink composition comprising a quinacridone pigment selected from the group consisting of CI Pigment Red 209 or a quinacridone solid solution pigment formed from at least two selected from the group, and having a pigment concentration lower than that of the magenta ink composition;
C. I. A light cyan ink composition comprising Pigment Blue 15: 3 as a pigment and having a pigment concentration lower than that of the cyan ink composition.

(2) The pigment contained in at least one of the magenta ink composition and the light magenta ink composition is C.I. I. Pigment violet 19, C.I. I. Pigment red 122, C.I. I. Pigment red 202 and C.I. I. The ink set according to (1) above, which is a quinacridone solid solution pigment formed from at least two selected from the group consisting of CI Pigment Red 209.
(3) The pigment contained in at least one of the magenta ink composition and the light magenta ink composition is C.I. I. Pigment violet 19 and C.I. I. The ink set according to (2) above, which is a quinacridone solid solution pigment formed from CI Pigment Red 202.
(4) In the quinacridone solid solution pigment, C.I. I. Pigment Violet 19 has a mass of C.I. I. The ink set according to (3) above, wherein the ink set is larger than the mass of the pigment red 202.

(5) In the quinacridone solid solution pigment, C.I. I. Pigment violet 19 / C.I. I. The ink set according to (3) or (4) above, wherein the pigment red 202 has a mass ratio of 70/30 to 50/50.
(6) C.I. contained in the quinacridone solid solution pigment. I. The ink set according to any one of (1) to (5) above, wherein the pigment violet 19 is γ type.
(7) The ink set according to any one of (1) to (6) above, wherein the pigment concentration of the light magenta ink composition and the light cyan ink composition is 2% by mass or less.
(8) The above (1) to (7), comprising a cyan ink composition, a magenta ink composition, a yellow ink composition, a light magenta ink composition, a light cyan ink composition, and a black ink composition. The ink set according to any one of the above.
(9) A recording apparatus comprising the ink set according to any one of (1) to (8).
(10) A recording method using the ink set according to any one of (1) to (9).

  In the ink set of the present invention, a light cyan ink composition used for image recording in a high lightness region uses a pigment type different from the cyan ink composition that is a higher concentration ink than the light cyan ink composition. That is, the light cyan ink composition includes C.I. which is the pigment type of the cyan ink composition. I. Pigment Blue 15: 6 is a different pigment type from C.I. I. Pigment Blue 15: 3 is used. With this configuration, it is possible to form a high-quality image with excellent graininess in a high-brightness cyan region and green region where an image is recorded using the light cyan ink composition.

Therefore, according to the ink set of the present invention, the dark blue region where the L ^* value of the CIE standard, which has been impossible to reproduce in the past, is 20 or less, the a ^* value is 30 or more, and the b ^* value is −75 or less. Can be reproduced, and the color reproducibility of the green region is excellent, and further, a high-quality image with excellent graininess can be formed even in the high-brightness cyan region and green region.

The gamut of the ink sets of Example 1 and Comparative Examples 1 and 2 at L ^* = 20 is shown. The gamut of the ink sets of Example 2 and Comparative Examples 3 and 4 at L ^* = 20 is shown. The gamut in the L ^* = 10-90 of the ink set of the comparative example 3 and the comparative example 4 is shown The gamut of the ink sets of Example 2 and Comparative Example 3 at L ^* = 10 to 90 is shown. The gamut of the ink sets of Example 2 and Comparative Example 4 at L ^* = 10 to 90 is shown. 6 is a chart showing graininess in a green region of ink sets of Example 3 and Comparative Example 5. 6 is a chart showing graininess in a cyan region of ink sets of Example 3 and Comparative Example 5.

  Hereinafter, the cyan ink composition, magenta ink composition, yellow ink composition, light cyan ink composition, and light magenta ink composition constituting the ink set of the present invention will be described in detail.

1. Pigment C.I. used for the cyan ink composition in the present invention. I. Commercially available pigment blue 15: 6 (hereinafter abbreviated as “P.B.15: 6”) can be used.

  In addition, C.I. which is a quinacridone pigment used in a magenta ink composition and a light magenta ink composition. I. Pigment violet 19 (hereinafter abbreviated as “P.V.19”), C.I. I. Pigment Red 122 (hereinafter abbreviated as “PR 122”), C.I. I. Pigment Red 202 (hereinafter abbreviated as “PR 202”) and C.I. I. Commercially available pigment red 209 (hereinafter abbreviated as “PR209”) can also be used.

  The quinacridone solid solution pigment in the present invention is P.I. V. 19 (in the solid solution, γ-type PV19 is preferred from the viewpoint of color development), P.V. R. 122, P.I. R. 202 and P.I. R. And at least two selected from the group consisting of 209.

  The combination of two or more quinacridone compounds is not particularly limited, but in the present invention, P.I. V. 19 and P.I. R. 209, p. V. 19 and P.I. R. 122, or P.122. V. 19 and P.I. R. It is preferable that the solid solution pigment is a combination with P.202. V. 19 and P.I. R. A solid solution pigment comprising a combination with 202 is particularly preferred.

  P. V. 19 and P.I. R. The preferred mixing ratio in the solid solution pigment with 209 is P.P. V. 19: P. R. 209 is in the range of 10:90 to 90:10, more preferably in the range of 15:85 to 85:15, and particularly preferably in the range of 30:70 to 50:50. P.P. V. 19: P. R. 122 is in the range of 10:90 to 90:10, more preferably in the range of 15:85 to 85:15, and particularly preferably in the range of 30:70 to 50:50. P.P. V. 19: P. R. 202 is in the range of 10:90 to 90:10, more preferably in the range of 15:85 to 85:15, and particularly preferably in the range of 30:70 to 50:50. By forming the quinacridone pigment into the above-mentioned solid solution pigment, a magenta ink composition and a light magenta ink composition excellent in color reproducibility of a high color and high brightness red region and in a purple region are formed. Is possible. Among these, P.I. V. 19 and P.I. R. 202, a solid solution pigment. V. A mass of 19 R. A pigment larger than the mass of 202 is particularly excellent in color reproducibility of a high color and lightness in a red region and in a purple region.

  The production method of the quinacridone solid solution pigment is not particularly limited, and generally known production methods can be used. Specifically, the methods disclosed in JP-A-11-49998, JP-A-2000-319534, and JP-A-2003-253150 can be mentioned. The quinacridone solid solution pigment in the present invention means a pigment that exists as a mixed crystal (a state crystallized in a mixed state) of a plurality of quinacridone pigment molecules. It is different from the one mixed with.

  Whether or not a solid solution pigment composed of two or more quinacridone pigments is formed can be easily confirmed by X-ray diffraction analysis. In the case of a simple mixture of two quinacridone pigments, the X-ray diffraction pattern is a pattern corresponding to the superposition of the X-ray diffraction patterns of the respective pigments, and the peak intensity is proportional to the blending ratio. On the other hand, when a quinacridone pigment solid solution is formed, it shows a diffraction pattern unique to the newly formed crystal.

  In the present invention, the quinacridone solid solution pigment preferably has an average particle size of the solid solution pigment in the range of 10 to 200 nm. More preferably, the average particle size is 50 to 150 nm. When the average particle size is less than 10 nm, the weather resistance may be deteriorated.

  Further, C.I. used in the yellow ink composition. I. Pigment yellow 74 (hereinafter abbreviated as “P.Y.74”), C.I. I. Pigment yellow 213 (hereinafter abbreviated as “P.Y.213”), C.I. I. Commercially available pigment yellow 185 (hereinafter abbreviated as “P.Y.185”) can also be used.

  Further, C.I. used in the light cyan ink composition. I. Commercially available pigment blue 15: 3 (hereinafter abbreviated as “P.B.15: 3”) can be used.

The pigment content in the cyan ink composition, magenta ink composition, and yellow ink composition in the present invention is 0.1 to 15 from the viewpoint of ink reliability such as ejection stability, storage stability, and clogging. It is preferable that it is mass%, and it is more preferable that it is 1-10 mass%.
In addition, the light cyan ink composition and the light magenta ink composition in the present invention are each an ink composition having a pigment concentration lower than that of a similar color ink composition, and the pigment concentration is 2 mass from the viewpoint of gradation and granularity. % Or less, and more preferably 1.5 to 0.3% by mass.

2. Components other than Pigment Components other than the pigment contained in each ink composition in the present invention are not particularly limited, but preferably contain the following components.

The dispersant that can be used for the pigment ink can be used without particular limitation, and examples thereof include a cationic dispersant, an anionic dispersant, a nonionic dispersant, and a surfactant.
Examples of anionic dispersants include polyacrylic acid, polymethacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid Copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer, Styrene-α-methylstyrene-acrylic acid-mono-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer , Vinyl acetate-maleic acid ester Examples include copolymers, vinyl acetate-crotonic acid copolymers, vinyl acetate-acrylic acid copolymers, and the like. Nonionic dispersants include polyvinyl pyrrolidone, polypropylene glycol, vinyl pyrrolidone-vinyl acetate copolymer, and the like. Surfactants as dispersants include anionic surfactants such as sodium dodecylbenzene sulfonate, sodium lactylate, ammonium salt of polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, poly Nonionic surfactants such as oxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, and the like. In particular, it is preferable to use a styrene- (meth) acrylic acid copolymer from the viewpoint of enhancing the dispersion stability of the pigment. As the dispersant, a water-insoluble vinyl polymer that imparts fixing properties and glossiness as described in JP-A No. 2007-186642 may be used.

In addition, each ink composition in the present invention preferably contains one or more polyhydric alcohols having a polyhydric alcohol, a saccharide, and an ethylene oxide chain as a wetting agent. By adding a wetting agent, when used for inkjet recording, the ink is prevented from drying and clogging at the head of the inkjet printer is suppressed.
Examples of the wetting agent include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylolethane, Polyhydric alcohols such as trimethylolpropane; sugars such as sugar alcohol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol mono Ethyl ether, triethylene glycol monobutyl ether Polyhydric alcohols having an ethylene oxide chain such as ether, and the like, these one or more is used.

  Each ink composition in the present invention preferably contains one or more pyrrolidones, alkanediols, and glycol ethers as a penetrant. By adding a penetrating agent, it is possible to increase the wettability of the recording medium and increase the penetrability of the ink. Examples of penetrants include pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone; alkane diols such as 1,2-pentanediol and 1,2-hexanediol; ethylene glycol monomethyl ether and diethylene glycol monoethyl Glycol ethers such as ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and the like, and it is preferable to include one or more of these.

  Moreover, each ink composition in the present invention preferably contains one or more compounds selected from the group consisting of acetylene glycols and polysiloxanes as a surfactant. By adding a surfactant, it is possible to increase the wettability of the recording medium and increase the permeability of the ink.

  Further, each ink composition in the present invention may contain a low boiling point organic solvent from the viewpoint of shortening the drying time of the ink. Examples of the low boiling point organic solvent include methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, sec-butanol, tert-butanol, iso-butanol, n-pentanol and the like. These 1 type (s) or 2 or more types are used. In particular, monohydric alcohol is preferable.

  Each ink composition in the present invention preferably contains components such as the pigment, dispersant, wetting agent, low-boiling organic solvent, penetrating agent, and surfactant described above, and preferably contains water as a balance. It is preferable to use pure water or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, or distilled water. In particular, water obtained by sterilizing these waters by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of capsi and bacteria is prevented over a long period of time.

  In each ink composition of the present invention, if necessary, a fixing agent such as a water-soluble rosin, an antiseptic / preservative such as sodium benzoate, an antioxidant / ultraviolet absorber such as an allophanate, a chelating agent Additives such as oxygen absorbers and pH adjusters can be contained, and one or more of these can be used.

3. Ink set The ink set of the present invention is capable of a wide range of color reproducibility, so that a yellow ink composition, a magenta ink composition, a cyan ink composition, a light cyan ink composition, a light magenta ink composition, and a black ink composition are used. It is preferable to provide at least a thing.
When the ink set of the present invention includes a black ink composition, the color material is not particularly limited, but examples of the color material included in the black ink composition include furnace black, lamp black, acetylene black, and channel black. Carbon blacks (CI Pigment Black 7), etc., or metals such as copper oxide and iron oxide (CI Pigment Black 11), aniline black (CI Pigment Black 1), etc. Although organic pigments are mentioned, carbon black having a relatively low specific gravity and difficult to settle in water is preferred for inkjet use. You may use these as 1 type or a 2 types of mixture. Specific examples of the pigment include carbon black, No. manufactured by Mitsubishi Chemical Corporation. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B, etc. are Raven 5750, 5250, 5000, 3500, 1255, 700, etc. made by Columbia, and Regal 400R, 330R, 660R, Mogu L, 700, Monarch 800, 880, made by Cabot, 900, 1000, 1100, 1300, 1400, etc. are Degussa Color Black FW1, FW2, FW2V, FW18, FW200, ColorBlack S150, S160, S170, Printex 35, U, the same V, the same 140 U, the Special Black 6, the same 5, the same 4 A, the same 4, and the like. Various components of the black ink composition and the adjustment thereof can be performed in the same manner as the other ink compositions described above.

4). Recording method and recording apparatus The use of the ink set according to the present invention is not particularly limited, but can be applied to various ink jet recording systems. Examples of the ink jet recording method include thermal jet ink jet, piezo ink jet, continuous ink jet, roller application, and spray application. Further, the ink set according to the present invention can be applied to a recording apparatus to which these recording methods are applied.

  In the present invention, glossy paper for ink jet recording is preferably used as a recording medium to which the droplets of the ink set according to the present invention are attached. Here, “glossy paper” refers to a paper in which an ink-receiving layer having excellent surface gloss is formed by applying a special coating to the surface of plain paper. In general, there are cast glossy paper in which an ink receiving layer is formed by a casting method to give gloss to the surface, and polymer-coated glossy paper in which an ink jet recording layer mainly composed of a resin is formed. As other polymer-coated glossy paper, a recording medium using an electron beam curable resin can also be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these.

1. Preparation of various ink compositions (C1, C2, C3, M1, M2, Y1, LC1, LC2, LM1, K1)
As shown in Table 1 below, cyan ink composition (C1, C2, C3), magenta ink composition (M1, M2), yellow ink composition (Y1), light cyan ink composition (LC1, LC2), light magenta ink A composition (LM1) and a black ink composition (K1) were prepared. In Table 1, the addition amount of each composition is mass%. Further, the “dispersing agent” used in Table 1 is a styrene-acrylic copolymer, and the “surfactant” is BYK-348 manufactured by Big Chemie Japan Co., Ltd.

  Further, the quinacridone solid solution pigment contained in the magenta ink composition M2 and the light magenta ink composition LM1 is a solid solution of γ-type PV19 and PR202, and γ-type PV19. And a pigment having a mass ratio of P.R.202 of 70:30 was prepared. The hue of the obtained solid solution pigment was magenta, but the X-ray diffraction pattern was different from the diffraction pattern of the mixture of γ-type PV19 and PR202.

2. 2. Evaluation of ink set 2-1. Evaluation of Color Reproduction Region Printing was performed using an inkjet printer (“PX-5500” manufactured by Seiko Epson Corporation). Ink cartridge for cyan (model number ICC37, manufactured by Seiko Epson), magenta ink cartridge (model number ICM37, manufactured by Seiko Epson), yellow ink cartridge (model number ICY37, manufactured by Seiko Epson), black Dedicated ink cartridges (model number ICBK33, manufactured by Seiko Epson) were filled with the ink compositions in the combinations shown in Table 2 to form ink sets of Examples and Comparative Examples.

The ink cartridge thus produced was installed in a printer, and a printing test was performed on glossy paper for photography (“Photo Paper <Glossy>” manufactured by Seiko Epson Corporation). The printing was a mixed color solid pattern with a duty of 85% or less.
The black ink was used for fine adjustment of brightness.

In this specification, “duty” is a value calculated by the following equation.
duty (%) = number of actual printing dots / (vertical resolution × horizontal resolution) × 100
(Where “number of actual print dots” is the number of actual print dots per unit area, and “vertical resolution” and “horizontal resolution” are resolutions per unit area. 100% duty is a single color for a pixel. The maximum ink mass).

In accordance with JIS Z8729, using a colorimeter (Spectrolino (manufactured by GretagMacbeth)), the coordinates of the L ^* a ^* b ^* color system of the color difference display method defined by CIE of the obtained printed matter were measured. . FIG. 1 shows the gamut of Example 1 and Comparative Examples 1 and 2 at L ^* = 20, and FIG. 2 shows the gamut of Example 2 and Comparative Examples 3 and 4 at L ^* = 20. Note that “VM” shown in FIG. 2 corresponds to the magenta ink M2.

As is clear from FIG. 1, in the dark blue region where L ^* is 20 or less, P.I. B. 15: 6 or P.I. B. A cyan ink composition containing No. 60 is combined with a magenta ink composition containing a quinacridone pigment, so that the conventional P.I. B. As compared with the case where the cyan ink composition containing 15: 3 was used, the color reproduction region could be greatly expanded. In addition, as shown in FIG. B. By combining a cyan ink composition containing 15: 6 with a magenta ink composition containing a quinacridone solid solution pigment (VM) as a pigment, an L ^* value that was previously impossible to reproduce was 20 or less, and an a ^* value was A color of 30 or more and a b ^* value of −75 or less could be realized.

3, 4, and 5 are gamuts of ink sets of Example 2, Comparative Example 3, and Comparative Example 4. FIG. 3 to 5, a ^* represents a position between the colors red and green, a negative value indicates green, and a positive value indicates red. Therefore, the larger the negative value in a ^* , the wider the color reproduction range of the green region. The color of the green region is different from that of various cyan ink compositions and P.I. Y. Reproduced with a yellow ink composition (Y1) containing 74 pigments.

3, the gamut of the ink set of Comparative Example 4 (ink set containing P.B.60 in the cyan ink composition) is colorless, and the ink set of Comparative Example 3 (P.B.15 in the cyan ink composition). : Ink set including 3) gamut is shown in black, and the common part of both gamuts is shown by shading.
As is clear from FIG. B. The ink set of Comparative Example 3 using 15: 3 pigment has a color reproducibility in the dark blue region of P.I. B. Although it was inferior to that using 60 pigment (Comparative Example 4) (see FIGS. 1 and 2), it showed good color reproducibility in the green region. For example, in the region where L ^* is 10 to 40, there are many black regions in the region where a ^* is negative. B. The ink set using the 15: 3 pigment (Comparative Example 3) B. This indicates that the color reproducibility is wider in the green region than the ink set using 60 pigment (Comparative Example 4).

On the other hand, in FIG. 4, the gamut of the ink set of Example 2 (ink set containing PB 15: 6 in the cyan ink composition) is colorless, and the ink set of Comparative Example 3 (in the cyan ink composition). The gamut of the ink set including P.B.15: 3 is shown in black, and the common part of both gamuts is shown by shading.
As is apparent from FIG. B. The ink set of Example 2 using 15: 6 pigment is excellent in color reproducibility in the dark blue region and also in the green region. B. It shows that it has a wide color reproducibility equivalent to that of the ink set of Comparative Example 3 using 15: 3 pigment.

In FIG. 5, the gamut of the ink set of Example 2 (ink set containing P.B.15: 6 in the cyan ink composition) is colorless, and the ink set of Comparative Example 4 (P.B. in the cyan ink composition). The gamut of the ink set including .60 is shown in black, and the common part of both gamuts is shown by shading.
FIG. 5 shows that P.P. B. The ink set using the 15: 6 pigment is better for P.I. B. It is clear that the color reproducibility is wider than the ink set using 60 pigments.

2-2. Graininess Evaluation in High Brightness Region Next, printing was performed using an inkjet printer (“PX-5500” manufactured by Seiko Epson Corporation). Ink cartridge for cyan (model number ICC37, manufactured by Seiko Epson), magenta ink cartridge (model number ICM37, manufactured by Seiko Epson), yellow ink cartridge (model number ICY37, manufactured by Seiko Epson), black Special ink cartridge (model number ICBK33, manufactured by Seiko Epson Corporation), light cyan dedicated ink cartridge (model number ICLC37, manufactured by Seiko Epson Corporation), light magenta dedicated ink cartridge (model number ICLM37, manufactured by Seiko Epson Corporation) Each ink composition was filled to form ink sets of Examples and Comparative Examples.

The ink cartridge thus prepared is mounted on a printer, and 14 points of green and cyan L ^* are 50 to 95 on glossy paper for photography (“Photo Paper <Glossy>” manufactured by Seiko Epson Corporation). A gradation patch with the image as the evaluation image was printed. The obtained printed matter was taken in as electronic data with a scanner (“GT-X770” manufactured by Seiko Epson Corporation), and the granularity index value was calculated with dedicated software. The scan resolution was 1200 dpi, and the analysis target area was 256 × 256 pixels.

FIG. 6 is a chart showing the results of the evaluation of graininess for the 14 types of evaluation images in the green region. FIG. 7 is a chart showing the results of evaluating the graininess of 14 types of evaluation images in the cyan region.
The graininess is evaluated based on the graininess index value GF shown in the following equation 1 using the dedicated software. Here, u is the spatial frequency, WS (u) is the winner spectrum of the image, VTF (u) is the visual sensitivity characteristic with respect to the spatial frequency, and L is the observation distance (300 mm). Further, (L ^* + 16/116) ^0.8 is a coefficient for adjusting the index value to the characteristics of human vision.

  Here, the meaning of the mathematical formula shown in the above equation 1 will be briefly described. WS (u) can be considered to represent the periodicity of the image. For example, when considering an image in which large black circle figures are repeatedly printed periodically, WS (u) of the image has a spatial frequency u1 corresponding to the diameter of the black circle and a space corresponding to the cycle in which the black circle is repeated. A large peak appears at the frequency u2. Conversely, if a WS (u) spectrum peak appears at spatial frequencies u1 and u2, it is considered that the image contains two periodic structures corresponding to the respective spatial frequencies. Can do.

Further, it is known that human vision has different sensitivities depending on the spatial frequency, and there exists a spatial frequency up having the highest sensitivity. In other words, human sensitivity increases as the spatial frequency is closer, and conversely, sensitivity decreases as the distance from the spatial frequency is higher. Accordingly, in an image in which black circles are repeatedly formed, the black circles are more noticeable as the spatial frequency u1 due to the diameter of the black circles or the spatial frequency u2 due to the period of the black circles is closer to the spatial frequency up. Conversely, as these spatial frequencies u1 and u2 become farther from the spatial frequency up, the black circle becomes less noticeable. In addition, the blackness of the black circle naturally affects the conspicuousness. That is, for black circles of the same size, darker black circles formed with darker inks such as K ink than lighter colored black circles formed with thin inks such as LK ink and LLK ink, It can be said that it stands out easily. The effect of the blackness of the black circle is reflected as the size of WS (u). This WS (u) is calculated by color-converting the scanned image data, applying a two-dimensional FFT to the L ^* component image, and then converting it to a music coordinate system to make it one-dimensional. .

  The evaluation formula according to the above mathematical formula 1 is a numerical value of the graininess based on such human visual characteristics. In other words, WS (u) representing the periodicity of an image is weighted by human vision and integrated at a spatial frequency, thereby converting the dot conspicuousness (image granularity) into a numerical value as a granularity index GF. (Reference: Makoto Fujino, Japanese Imaging Society “Japan Hardcopy '99” P.291-294).

6 and 7, it can be seen that the larger the L ^* is, the larger the granularity index is and the worse the granularity is. In particular, in a high brightness region where L ^* is 80 or more, P.B. It can be seen that the use of 15: 3 can significantly suppress the deterioration of graininess.

As described above, according to the ink set of the present invention, the dark portion where the L ^* value of the CIE standard, which has been impossible to reproduce in the past, is 20 or less, the a ^* value is 30 or more, and the b ^* value is −75 or less. It is clear that the color of the blue region can be reproduced, the color reproducibility of the green region is excellent, and further, a high-quality image with excellent graininess can be formed even in the high-brightness cyan region and green region.

Claims (8)

C. I. A cyan ink composition containing Pigment Blue 15: 6 as a pigment;
C. I. Pigment violet 19 or C.I. I. Pigment violet 19 and C.I. I. A magenta ink composition comprising a quinacridone solid solution pigment formed from CI Pigment Red 202 ;
C. I. And a yellow ink composition containing Pigment Yellow 7 4,
C. I. Pigment Violet 19 and C.I. I. It includes quinacridone solid solution pigment formed Pigment Red 20 2 or, et al., And low light magenta ink composition having a pigment concentration than and the magenta ink composition,
C. I. A light cyan ink composition comprising Pigment Blue 15: 3 as a pigment and having a pigment concentration lower than that of the cyan ink composition . In the quinacridone solid solution pigment, C.I. I. Pigment Violet 19 has a mass of C.I. I. The ink set according to claim 1 , wherein the ink set is larger than a mass of the pigment red 202. In the quinacridone solid solution pigment, C.I. I. Pigment violet 19 / C.I. I. The ink set according to claim 1 or 2 , wherein the pigment red 202 has a mass ratio of 70/30 to 50/50. C.I. contained in the quinacridone solid solution pigment. I. The ink set according to any one of claims 1 to 3 , wherein the pigment violet 19 is γ-type. The ink set according to any one of claims 1 to 4 , wherein the light magenta ink composition and the light cyan ink composition have a pigment concentration of 2% by mass or less. Cyan ink composition, a magenta ink composition, yellow ink composition, light magenta ink composition, characterized by comprising a light cyan ink composition and black ink composition, to any one of claims 1 to 5 The ink set described. Recording apparatus comprising the ink set according to any one of claims 1-6. Recording method characterized by using the ink set according to any one of claims 1-6.

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